Disk drive device with hub

ABSTRACT

The disk drive device includes a base member, a hub, a bearing unit which is arranged on the base member and which rotatably supports the hub, and a spindle drive unit which drives the hub to rotate. The spindle drive unit includes a stator core having a salient pole, a coil wound around the salient pole and a magnet opposed to the salient pole. The hub formed of magnetic material includes an outer cylinder portion engaged with an inner circumference of a recording disk and an inner cylinder portion to which an outer circumference of the magnet is fixed. The diameter of the inner cylinder portion is larger than the diameter of the outer cylinder portion.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a Divisional Application based on U.S. Ser. No.12/545,751, filed on Aug. 21, 2009, the entire contents of which isincorporated herein by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a disk drive device having a hub onwhich a recording disk is mounted.

2. Description of the Related Art

Recently, a disk drive device such as an HDD has been improved inbearing stiffness by incorporating a dynamic pressure fluid bearingunit. There is a case that such a disk drive device having the dynamicpressure fluid bearing unit is mounted on a small portable apparatus. Aportable apparatus is desired to be further thinned and lightened.Therefore, the disk drive device which is mounted on the portableapparatus is desired to be further thinned and lightened.

For example, patent document 1 has disclosed a disk drive device havinga dynamic pressure fluid bearing unit with a first radial dynamicpressure groove of which the formed width in the axial direction isnarrower than that of a second radial dynamic pressure groove.

-   Patent document 1: Japanese Patent Application Laid-Open No.    2007-198555

In order to thin a disk drive device, it is necessary to thin a spindledrive unit and dynamic pressure fluid bearing unit of the disk drivedevice. Here, when the spindle drive unit is further thinned, there maybe a case that the rotation becomes unstable due to a decrease intorque. Further, when the dynamic pressure fluid bearing unit is furtherthinned, there may be a case that rotation of the disk becomes unstabledue to a decrease in the stiffness of the dynamic pressure fluid bearingunit. When the rotation becomes unstable as mentioned above, there maybe a case, at the very worst, where the normal reading/writing operationof magnetic data cannot be performed.

SUMMARY OF THE INVENTION

The present invention is devised in view of the abovementionedsituation, and a purpose thereof is to provide a disk drive device thatstably rotates a recording disk while being further thinned.

In view of the above mentioned, a disk drive device according to anaspect of the present invention includes a base member, a hub, a bearingunit that is arranged on the base member and that rotatably supports thehub, and a spindle drive unit that drives the hub to rotate. The spindledrive unit includes a stator core having a salient pole, a coil woundaround the salient pole, and a magnet opposed to the salient pole. Thehub formed of magnetic material includes an exterior cylinder portionengaged with an inner circumference of a recording disk and an interiorcylinder portion to which an outer circumference of the magnet is fixed.The diameter 90 of the interior cylinder portion of the hub is largerthan the diameter 92 of the exterior cylinder portion of the hub.

According to this aspect, the diameter of the magnet can be larger thanthe inner circumference of the recording disk by setting the diameter 90of the interior cylinder portion to be larger than the diameter 92 ofthe exterior cylinder portion. Thus, even with the thinned disk drivedevice, the magnet can be ensured to be sufficient size so as tosuppress a decrease in torque. Accordingly, the rotation of therecording disk can be stabilized.

BRIEF DESCRIPTION OF THE DRAWINGS

Embodiments will now be described, by way of example only, withreference to the accompanying drawings which are meant to be exemplary,not limiting, and wherein like elements are numbered alike in severalFigures.

FIG. 1A is a view illustrating a disk drive device according to anembodiment.

FIG. 1B is a view illustrating the disk drive device according to thepresent embodiment.

FIG. 2 is a sectional view of a part of the disk drive device accordingto the present embodiment.

FIG. 3 is a sectional view of a hub according to the present embodiment.

FIG. 4 is a sectional view of a part of a disk drive device according tothe related art.

FIG. 5A is a view illustrating a method of forming a coil according tothe present embodiment.

FIG. 5B is a view illustrating the method of forming a coil according tothe present embodiment.

FIG. 5C is a view illustrating the method of forming a coil according tothe present embodiment.

FIG. 6 is a schematic view schematically illustrating behavior ofmomentary vibration of a recording disk surface.

DETAILED DESCRIPTION OF THE INVENTION

The invention will now be described by reference to the preferredembodiments. This does not intend to limit the scope of the presentinvention, but to exemplify the invention.

In the following, the same numeral is given to the same or a similarstructural element or member, which is illustrated in each of thedrawings, and redundant description will not be repeated. For ease ofunderstanding, members of each of the drawings are appropriatelyenlarged or reduced in scale Here, in the following description, theterms “lower” and the “upper” in regard to the drawings are respectivelyexpressed as the “bottom” and the “top”, for convenience.

FIGS. 1A and 1B illustrate a disk drive device 100 according to anembodiment. FIG. 1A is a top view of the disk drive device 100 and FIG.1B is a side view of the disk drive device 100. Here, FIG. 1Aillustrates a state where a top cover 2 is removed. Further, FIG. 2 is asectional view of a part of the disk drive device 100 according to thepresent embodiment. Furthermore, FIG. 3 is a sectional view of a hub 4according to the present embodiment. Each of FIG. 2 and FIG. 3 is theview sectioned at line A-B in FIG. 1A.

The disk drive device 100 includes a chassis 10, which has a base member3 and a looped circumference wall portion 15, the hub 4 to which aring-shaped recording disk 1 is mounted, a bearing unit 5, which isarranged on the base member 3 so as to rotatably support the hub 4, aspindle drive unit 6, which drives the hub 4 to rotate, a head driveunit 17, the top cover 2, and a screw 9. Further, the disk drive device100 includes a fixed body portion 7 configured with members that do notrotate and a rotating body portion 8 configured with members thatrotate. The fixed body portion 7 and the rotating body portion 8 includethe bearing unit 5, which supports the hub 4 in order to be relativelyrotatable, and the spindle drive unit 6, which drives the hub 4 torotate.

The chassis 10 includes the base member 3, which is a plane area of ahollowed portion, and the looped circumference wall portion 15, which isformed in a wall shape at the outer circumference of the base member 3.The base member 3 has a bearing hole 3A into which a housing 13, asleeve 14, and a shaft 16 are inserted. The outer circumference surfaceof the looped circumference wall portion 15 is rectangularly formed. Theinner circumference surface of the looped circumference wall portion 15is formed by connecting a circular portion 15A for surrounding therecording disk 1 and a rectangular portion 15B for surrounding an areato which the head drive unit 17 is mounted. The looped circumferencewall portion 15 functions as a support member of the disk drive device100 for supporting in the rotation axial direction of the shaft 16. Onthe other hand, the base member 3 functions as a support member of thedisk drive device 100 for supporting in the direction perpendicular tothe rotation axial direction of the shaft 16.

The top cover 2, which is illustrated in FIG. 1B, is arranged and fixedat the upper end of the looped circumference wall portion 15 by screwingthe screw 9 into a screw hole 15C, which is formed at the upper endsurface side of the looped circumference wall portion 15. A clean airchamber is formed by being enclosed with the chassis 10 and the topcover 2 for covering the hollow portion of the chassis 10. The clean airchamber is filled with clean air from which particles are removed. Therecording disk 1, which is a magnetic recording medium, the rotatingbody portion 8, and the head drive unit 17 are arranged in the clean airchamber.

As shown in FIG. 2, the bearing unit 5 is arranged on the base member 3and includes the shaft 16, the sleeve 14, the housing 13, an overhangingmember 19, and a descent portion 20. Further, the bearing unit 5includes a radial dynamic pressure groove 22, a thrust dynamic pressuregroove 23, and a capillary seal portion 24.

The shaft 16 functions as the rotation axis. The upper end of the shaft16 is fixed to a shaft hole 4M, which is formed at the center of the hub4. The shaft 16 is inserted into the sleeve 14. The sleeve 14, which isapproximately cylindrical, is inserted into the housing 13. A part ofthe surface of the outer circumference of the sleeve 14 is fixed to thesurface of the inner circumference of the housing 13 by bonding and thelike. The overhanging member 19, which overhangs outward in the radialdirection, is fixed to an opening end surface 14A at the upper side ofthe sleeve 14. The overhanging member 19 restricts the movement of thehub 4 in the axial direction in cooperation with the descent portion 20.Further, the overhanging member 19 and the descent portion 20 preventthe rotating body portion 8 from coming out of place.

The housing 13 is in the form of a cup, with a bottom, such that acylinder portion and a bottom portion are integrally formed. A part ofthe surface of the outer circumference of the housing 13 is fixed to abearing hole 3A, which positions is positioned approximately at thecenter of the base member 3. The bottom portion of the housing 13 isformed at the lower end of the housing 13 for sealing so that lubricantdoes not leak to the outside of the housing 13.

The radial dynamic pressure groove 22 and the thrust dynamic pressuregroove 23 function as the bearing to rotatably support the hub 4. Twoherringbone-shaped radial dynamic pressure grooves 22 are formed to bevertically apart, at least at either of the inner circumferentialsurface of the sleeve 14 or the outer circumferential surface of theshaft 16. Further, the thrust dynamic pressure grooves 23, which areherringbone-shaped or spiral-shaped, are formed at both a surface of thedescent portion 20 opposed to the surface of the opening end of thehousing 13 and the upper surface of the descent portion 20 opposed to alower surface of the overhanging member 19. Here, the thrust dynamicpressure grooves 23 may be formed at least at either the opening endsurface 14A of the sleeve 14 or the lower end surface 4F of the hub 4,which is opposed to the opening end surface 14A.

When the shaft 16 is rotated, a radial dynamic pressure is generated atthe lubricant by the radial dynamic pressure groove 22, so that therotating body portion 8 is supported in the radial direction. Further,when the descent portion 20 is rotated, a thrust dynamic pressure isgenerated at the lubricant by the thrust dynamic pressure groove 23, sothat the rotating body portion 8 is supported in the axial thrustdirection.

The capillary seal portion 24 is formed with the inner circumferencesurface of a cylinder portion of the descent portion 20 and the outercircumference surface of the housing 13 so that the gap between theinner circumference surface of the descent portion 20 and the outercircumference surface of the housing 13 gradually becomes larger towardthe opening end at the lower side of the descent portion. The lubricantsuch as oil is infused to a space defined by the radial dynamic pressuregroove 22 and the opposing surface thereto, the thrust dynamic pressuregroove 23 and the opposing surface thereto, and the capillary sealportion 24. The boundary liquid level at which the lubricant contactsoutside air is set at some mid-part of the capillary seal portion 24.The capillary seal portion 24 prevents leaking of the lubricant withcapillarity.

The spindle drive unit 6 includes a stator core 11 that is fixed to thebase member 3, a three-phase coil 12, which is wound around a salientpole of the stator core 11, and an approximately cylindrical magnet 21,which is fixed at an interior cylinder portion 4D of the hub 4, as seenin FIG. 4.

The stator core 11 includes a circular portion and nine salient polesthat are extended in the radial direction therefrom. The stator core 11is formed by performing insulation coating such as electro-depositioncoating and powder coating on the surface thereof after a plurality ofmagnetic plates such as ferrosilicon plates are laminated. The magnet 21is formed of rare-earth material such as Nd—Fe—B(neodymium-ferrum-boron), for example. Rustproofing such aselectro-deposition coating and spray coating is performed on the surfaceof the magnet 21. Further, for example, the magnet 21 has drivingmagnetic poles of twelve poles along the circumferential direction of aportion of the inner circumference of the magnet 21. The magnet 21opposes to distal ends 11A of the salient poles of the stator core.

For the coil 12, a wire 25 is wound a predetermined number of timesaround the salient pole of the stator core 11 from the lower side of thesalient pole, and then, is wound around the adjacent salient pole of thestator core 11 from the upper side of the salient pole. After the wire25 is continuously wound a predetermined number of times around thesalient poles of the stator core 11 in this manner, the wound end of thewire 25 is drawn to the lower side of the salient pole of the statorcore 11. Subsequently, the wound end of the wire 25 is drawn to theopposite side of the base member 3 through a wire hole 3B, which isdisposed at the base member 3, and then, electrically connected to awiring member 26 which is arranged at the lower surface of the basemember 3 in a concavity 26B. The wound end of the drawn wire 25 is fixedwith a bond so as not to be released. Such fixing prevents the wire 25from disconnection due to large-amplitude vibration caused by resonanceduring ultra-sonic cleaning. When the coil 12 is powered with athree-phase current of an approximate sine-wave by a predetermined drivecircuit via the wiring member 26, the coil 12 generates a magnetic fieldfor rotation at the salient poles of the stator core 11. A rotationaldriving force is generated by the interaction between the driving polesof the magnet 21 and the magnetic field for rotation so that therotating body portion 8 is rotated. Namely, the spindle drive unit 6drives the rotating body portion 8 to rotate.

The fixed body portion 7 is configured to include the chassis 10 ofwhich section is an approximate hollow shape, the stator core 11, thecoil 12, the housing 13, and the sleeve 14. Further, the rotating bodyportion 8 is configured to include the approximately pan-shaped hub 4 towhich the recording disk 1 is mounted, the shaft 16 and the magnet 21.

In the following, the hub 4 is specifically described with reference toFIG. 3. The hub 4 is formed of magnetic material such as SUS430F whichhas soft magnetism. It is preferable to form the whole hub 4 withmagnetic material in view of generating an effect of magnetic shield.The hub 4 is formed by machining, such as by pressing and cutting so asto create the predetermined shape of being approximately pan-shaped. Forexample, stainless steel DHS1 manufactured by Daido Steel Co. Ltd. ispreferable in view of resources expended. In addition, stainless steelDHS2 is further preferable in view of its excellent corrosionresistance.

The shaft hole 4M is formed at the center of the hub 4 and a circularcenter portion 4I is formed around the shaft hole 4M. The shaft hole 4Mis formed so that the dimension thereof in the axial direction is largerthan the dimension in the axial direction of a part of the centerportion 4I opposing to the upper end surface of the sleeve 14. A part ofthe outer circumference of the shaft hole 4M is projected downward.Accordingly, connecting surface between the hub 4 which is thinned andthe shaft 16 is ensured.

A circular stepped of two levels is formed at the upper end surface 4Aof the hub 4 and the center portion 4I is located at the top level. Arecess portion 4J which is lowered downward by one step from the centerportion 4I is formed at the top end surface 4A to be ring-shaped. Aplurality of threaded holes 4K are disposed at the upper surface of therecess portion 4J at the same circular intervals. A clamper 29 isdisposed on the recess portion 4J. Then, the circular step between thecenter portion 4I and the recess portion 4J is fitted to a center holeof the clamper 29. The clamper 29 is fixed by screwing screws 30 to thethreaded holes 4K.

A circular exterior cylinder portion 4B is formed as a stepped portionlowered from the periphery of the recess portion 4J. A annular extensionportion 4C is formed to extend outward in the radial direction from thelower end of the periphery of the exterior cylinder portion 4B. Theinner circumference of the center hole of the recording disk 1 isengaged with the exterior cylinder portion 4B of the hub 4 so that therecording disk 1 is mounted on the upper surface of the annularextension portion 4C. The annular extension portion 4C sags to the basemember 3 side. The outer circumference of the magnet 21 is fixed to theinterior cylinder portion 4D. The annular extension portion 4C, which islocated in an area outside the outer circumference of the magnet 21 inthe radial direction, functions as a back yoke for the magnet 21.

A circular projecting portion 4E, which projects in the direction towardthe base member 3 between the housing 13 and the stator core 11, isformed at the lower surface of the hub 4. The circular descent portion20 is fixed to the inner circumference surface of the circularprojecting portion 4E of the hub 4 through bonding.

A lower end surface 4F of the hub 4 opposing an opening end surface 14Aof the sleeve 14 is located at the back surface of the center portion4I. A portion 4H of the hub 4 opposing the coil 12 is located at theback surface of the recess portion 4J.

Here, a problem with respect to the related art, which is recognized bythe present inventor, is described based on the structure according toFIG. 4. FIG. 4 is a sectional view of a part of a disk drive device 200of the related art. When the disk drive device 200 of the related art isthinned, a spindle unit 52 such as a stator core 50 becomes thinaccordingly. When the spindle unit 52 becomes thin, the rotation becomesunstable due to torque decrease. When the rotation becomes unstable, theunstableness may impair normal read/write operation of magnetic data, atworst.

There may be a solution for recapturing a decrease in torque by using amagnet 54 with a larger diameter. However, with the configuration thatthe recording disk 1 is located at an area on the extension of the outercircumference of the magnet 54, a back yoke portion 58 of the hub 56sandwiched by the inner circumference of the recording disk 1, and theouter circumference of the magnet 54 becomes thin in accordance withincrease of the diameter of the magnet 54. The back yoke portion 58constitutes a part of a magnetic circuit through which magnetic fluxdeparting from the outer circumference of the magnet 54. Thus, when theback yoke portion 58 becomes thin, magnetic saturation occurs. When themagnetic saturation occurs, the magnetic flux is hardly increased eventhough the magnetic field is strengthened. Accordingly, the torquecannot be increased since the increase of the magnetic flux contributingto the torque is slight. On the other hand, the magnetic flux leaking tothe recording disk 1 side is extremely increased. Therefore, with theconfiguration that the recording disk 1 is located at the area on theextension of the outer circumference of the magnet 54, there is apossibility that normal read/write operation of magnetic data isimpaired by the leaked magnetic flux. This has been an inhibitor ofthinning the disk drive device 200. Further, even in the case that theback yoke portion 58 is thickened in the related art, increase of thetorque is not expected since the magnet 54 has to be decreased in sizeaccordingly.

In view of the abovementioned problem, the recording disk 1 according tothe present embodiment is arranged at a position to be apart upward fromthe magnet 21 in the axial direction being away from the area on theextension of the outer circumference of the magnet 21 in the radialdirection, as illustrated in FIG. 2. With this configuration, themagnetic flux leaking to the recording disk 1 side can be decreased.Then, the interior cylinder portion 4D of the hub 4 is configured sothat the diameter 90 thereof is larger than the diameter 92 of theexterior cylinder portion 4B of the hub 4, as seen in FIG. 3. As aresult, it becomes possible to enlarge the outer circumference of themagnet 21 so that the torque is increased due to increase of themagnetic flux amount of the magnetic poles for driving. Accordingly, theconfiguration is preferable for the thinned disk drive device 100.Further, since the recording disk 1 is arranged at the upper position inthe axial direction away from the area on the extension of the outercircumference of the magnet 21 in the radial direction, the back yoke ofthe hub 4 can be configured to be sufficiently thick in the radialdirection. As a result, even in the case that the magnet 21 of which theenergy product is larger is used, the leak in magnetic flux can besuppressed and the torque can be increased.

The diameter 94 of a circle connecting the ends 11A of the salient polesof the stator core 11 may be set to be 80% or more of the diameter 92 ofthe exterior cylinder portion 4B of the hub 4. By configuring the statorcore 11 to be large, as mentioned above, more winding can be performedfor the coil 12 so that torque increase is expected. Here, when thediameter 94 of the circle connecting the salient ends 11A of the salientpoles of the stator core 11 exceeds 100% of the diameter 92 of theexterior cylinder portion 4B, the leaked magnetic flux of the magnet 21may affect the recording disk 1 and may impair the normal read/writeoperation of magnetic data. Therefore, the diameter of the circleconnecting the salient ends 11A of the salient poles of the stator core11 is within a range of 80% to 100% of the diameter 92 of the exteriorcylinder portion 4B.

The base member 3 has a wire hole 3B through which the wire 25 forforming the coil 12 is inserted. A drawing line of the wire 25 whichforms the coil 12 is introduced to exit through the wire hole 3B to theback surface 3C of the upper surface of the base member 3 on which thebearing unit 5 is arranged. In the related art of FIG. 4, the drawingline of the wire is connected to a wiring member 66 by soldering at aposition strictly below the position where the drawing line is drawnfrom the coil 12. The thickness of the wiring member 66 and the heightof the connection portion 68 at the position strictly below the coil 62are to be a barrier of thinning the spindle drive unit 5.

Next, in the disk drive device 200 of the related art which isillustrated in FIG. 4, a cylinder portion 76 and a bottom portion 78 ofthe housing is fixed by bonding as separate members. In this case, whenthe disk drive device is thinned, the bonding part also becomes thin.When the bonding part becomes thin, the connection strength isdecreased. Accordingly, there is a possibility of disconnection due toimpact.

Here, there is a case that the base member 3 is formed of metal such asaluminum. In this case, there is a possibility that the wire 25, whichis drawn to the lower surface 3C of the base member 3, may beelectrically short-circuited by directly contacting to the base member3. In order to cope with this problem, a channel portion 3D, whichintroduces the wire to exit through the wire hole 3B for connecting tothe wiring member 26, is disposed at the back surface 3C of the surfaceof the base member 3 to which the bearing unit 5 is disposed. Thechannel portion 3D is insulation treated. As a result, the problem thatthe wire 25 is electrical short-circuited with the base member 3 isrelieved. Further, by combining the positioning of the abovementionedconnection portion 26A with the configuration of positioning outside themagnet 21 in the radial direction, in concavity 26B, the spindle driveunit 6 can be thinned by the amount based on the thickness of the wiringmember 66 and the height of the connection portion 68 of the related artwhich is illustrated in FIG. 4. Here, for example, cationicelectro-deposition coating (hereinafter, called ED coating) onto thebase member 3, which is molded with aluminum die-casting, is preferableas the isolation process in view of less pin holes.

Here, when the disk drive device 100 is configured to be furtherthinned, the coil 12, which is wound around the salient poles and thelower surface of the hub 4, becomes extremely close. In this case, thepossibility that the coil 12 contacts the rotating hub 4 is increased.When the coil 12 contacts the hub 4, an electrical short-circuit mayoccur. In order to cope with this problem, the coil 12 is leveled sothat the surface opposing to the hub 4 and the surface opposing to thebase member 3 are to be level.

FIGS. 5A to 5C illustrate a forming method of the coil 12 according tothe present embodiment. FIG. 5A illustrates the coil 12 before forming,FIG. 5B illustrates the coil 12 during pressing, and FIG. 5C illustratesthe coil 12 after pressing. As illustrated in the drawings, the coil 12is formed by being pressed between a first pressing die 40 and a secondpressing die 42 after the wire 25 is wound around the salient poles ofthe stator core 11. The pressing surfaces of the first pressing die 40and the second pressing die 42 are flat. By forming the coil 12 to beflat with pressing, the dimension of the coil 12 in the axial directionis stabilized so that the possibility that the coil 12 comes in contactwith the rotating hub 4 can be decreased. Accordingly, the dimension ofthe coil 12 in the axial direction can be thinned.

Further, in order to cope with the contacting problem of the coil 12 tothe rotating hub 4, the flattening ratio of the wire 25, which forms theleveled coil 12, may be 90% or less. The flattening ratio of the wire 25is expressed by a percentage of the dimension “b” of the section of thesingle wire 25 in the axial direction against the dimension “a” in theradial direction. Here, the flattening ratio of the wire 25 of the coil12 is defined at a part of which the flattening ratio is the lowest. Theequation thereof is as follows:

The flattening ratio of the wire 25=(b/a)×100

When the coil 12 is formed with pressing so as to limit the dimension ofthe coil 12 in the axial direction, the part of the wire 25 of which theflattening ratio becomes lowest is the part that is thickest in theaxial direction. As a result, the possibility of contact of the coil 12to the rotating hub 4 is further decreased.

Furthermore, in order to cope with the contacting problem of the coil 12to the rotating hub 4, it is also possible to perform the insulationtreatment on the surface of the hub 4 opposing to the coil 12. As aresult, the possibility of the electrical short-circuiting, which causesa malfunction, is decreased. For example, a circular film 27 that ismade of Polyethylene terephthalate (PET) may be stuck with double-facedtape to the surface 96 of the hub 4 opposed to the surface 12A of thecoil 12. This method is preferable in view of easy operation.

Further, there may be a problem that an electrical short-circuit occursdue to the coil 12 coming in contact with the base member 3. In order tocope with this problem, it is also possible to perform an insulationtreatment on the surface 98 of the base member 3 opposed to the surface12B of the coil 12. As a result, the possibility that the coil 12 comesin contact with the base member 3 to cause an electrical short-circuitis decreased. For example, it is also possible to perform the ED coatingon the base member 3 which is molded with aluminum die-casting as theinsulation treatment. This is preferable in view of less pin holes.Further, a circular film 28, which is made of PET, may be stuck withdouble-faced tape to the surface of the base member 3 opposing to thecoil 12. This method is preferable in view of easy operation.

By the way, in the case that the disk drive device 100 is thinned,stiffness is decreased and rocking-mode resonance frequency is decreasedwhen the portion 4H of the hub 4 opposed to the coil 12 in the axialdirection is shortened. Here, the rocking-mode resonance is describedwith reference to FIG. 6. FIG. 6 is a schematic view, whichschematically illustrates behavior of momentary vibration of a recordingdisk 1 surface. In FIG. 6, dashed lines illustrate a nodal diameter 36and a nodal circle 38 at the vicinity of toque-ripple frequency. Thearea with hatching indicates that the vibration phase thereof at thevicinity of the torque-ripple frequency is reverse to that of the areawithout hatching. Solid lines are contour lines of vibrationdisplacement at the vicinity of the torque-ripple frequency.

The resonance of the disk drive device 100 during non-rotating has beenexamined in the state that the recording disk 1 is mounted in the diskdrive device 100. As a result, the rocking-mode resonance with thesingle nodal diameter 36 and the nodal circle 38 as an intermediateportion was observed in the recording disk 1 at the vicinity of thetorque-ripple frequency. Through the study of the present inventor, themain factors that determine the frequency of the rocking-mode resonanceare discovered to be the stiffness of the bearing, the stiffness of theconnecting portion between the hub 4 and the shaft 16, the stiffness ofthe connecting portion between the recording disk 1 and the hub 4, thestiffness of the recording disk 1 itself, the lateral moment of inertiaof the recording disk 1, and the lateral moment of inertia of the hub 4.

When the frequency of the rocking-mode resonance becomes low, there maybe a case that large vibration occurs due to resonance with thevariation of the drive torque. There may be a problem that suchvibration causes a malfunction of normal read/write operation ofmagnetic data, at worst. In order to cope with this problem, the width102 in the axial direction of the hub 4 opposed to the coil 12 may belarger than the width 104 in the axial direction of the base member 3opposed to the coil 12. This is for the relative relation of dimensionsof the base member 3 and the hub 4 in the axial direction in the casethat the disk drive device 100 is thinned. As a result, the problemcaused by decrease of the frequency of the rocking-mode resonance isrelieved.

Next, in the disk drive device 200 of the related art, which isillustrated in FIG. 4, a center part of a clamper 70 is fixed at thecenter of the shaft 74 with a screw 72. Therefore, the center part ofthe hub 56 is to be thinned in the axial direction by the amount of theclamper 70 and the screw 72. When the center part of the hub 56 isthinned in the axial direction, the frequency of rocking-mode resonancebecomes low. Accordingly, there may be a case that large vibrationoccurs due to the resonance with the variation of the drive torque.

In order to cope with this problem, in the disk drive device 100according to the present embodiment, the hub 4 includes the recessportion 4J, which is formed on the surface of the hub 4 at the side towhich the recording disk 1 is mounted, and the threaded hole 4K, whichis formed at the recess portion 4J, as illustrated in FIG. 2 and FIG. 3.The clamper 29 is fixed to the threaded hole 4K with the screw 30. As aresult, the problem caused by thinning the center portion 4I of the hub4 in the axial direction is relieved. In addition, since the shaft 16can be configured to be long, it is preferable because decrease of thebearing stiffness can be prevented.

Further, there may be a case that the dimension in the axial directionof the thread portion of the threaded hole 4K, which is formed at thehub 4, is insufficient. In order to cope with this problem, the threadedportion 4K is formed to penetrate in the axial direction. Further, acover member 31 is disposed at the surface 96 of the hub 4 to which thethreaded portion 4K is formed and which is opposed to the surface 12A ofthe coil 12. As a result, the problem that the dimension in the axialdirection of the thread portion of the threaded hole 4K is insufficientis relieved. A variety of materials can be used for the cover member 31.For example, a PET film may be stuck with double-faced tape to thesurface 98 of the base member 3 opposed to the surface 12B of the coil12. This method is preferable in view of easy operation as well asfunctioning as the insulation treatment against the coil 12.

Next, in the disk drive device 200 of the related art, which isillustrated in FIG. 4, a cylinder portion 76 and a bottom portion 78 ofthe housing is fixed by bonding as separate members. In this case, whenthe disk drive device is thinned, the bonding part also becomes thin.When the bonding part becomes thin, the connection strength isdecreased. Accordingly, there is a possibility of disconnection due toimpact.

In order to cope with this problem, in the disk drive device 100 of thepresent embodiment, the housing 13 is in the form of a cup with a bottomsuch that a cylinder portion and a bottom portion are integrally formed,as illustrated in FIG. 2. As a result, the problem of disconnectionbetween the cylinder portion and the bottom portion of the housing 13 isrelieved even when the disk drive device 100 becomes thin.

Next, in the disk drive device 200 of the related art which isillustrated in FIG. 4, a circular member 80 is fixed by bonding to theinner circumference of a circular projecting portion of the hub 56. Thedoughnut-shaped circular member 80 is formed so that the dimensionthereof in the axial direction is 1.2 mm or more for ensuring connectionstrength with the hub 56. When the disk drive device 200 becomes thin,the center portion of the hub 56 in the axial direction is to be thin bythe amount of the circular member 80. When the center portion of the hub56 in the axial direction becomes thin, the frequency of therocking-mode resonance becomes low. Accordingly, there may be a casethat large vibration occurs due to resonance with the variation of thedrive torque.

In order to cope with this problem, the bearing unit 5 of the presentembodiment includes the descent portion 20, which is rotated integrallywith the hub 4, and the overhanging member 19, which is arranged so asto be nonrotatable at a position opposed to the descent portion 20 inthe axial direction, as illustrated in FIG. 2. Further, it is alsopossible that the descent portion 20 restricts movement of the hub 4 incooperation with the overhanging member 19 and the width in the axialdirection of the descent portion 20 opposed to the overhanging member 19is set to be 0.6 mm or less. Namely, the thickness of a disk portion 20Aof the descent portion 20 is set to be 0.6 mm or less. As a result, inthe case that the disk drive device 100 is thinned, the dimension of thecenter portion 4I of the hub 4 in the axial direction can be ensured. Inaddition, it is preferable that the dimension of the descent portion 20is set to be 0.4 mm or less because the center portion 4I of the hub 4can be further thickened in the axial direction.

Further, when the circular member 80 of FIG. 4 is thinned in the axialdirection, there may be a problem of disconnection due to impact sincethe connection strength of the circular member 80 with the hub 56 isdecreased. In order to cope with this problem, the descent portion 20 isformed by integrating the disk portion 20A, which is opposed to theoverhanging member 19 in the axial direction, and a cylinder portion20B, which is connected to the periphery portion of the disk portion20A. With this configuration, the dimension in the axial direction forconnecting to the circular projecting portion 4E can be sufficientlyensured. As a result, the problem of disconnection between the descentportion 20 and the hub 4 is relieved. For example, by setting thedimension of the cylinder portion 20B in the axial direction to be 2.0mm or more, the connection strength with the hub 4 is sufficientlyensured. In addition, by setting the dimension of the disk portion 20Ain the axial direction to be 0.4 mm or less thereafter, the dimension ofthe center portion 4I of the hub 4 can be configured to be thick in theaxial direction.

There may be a problem that the machining of the descent portion 20requires much expense in time. In order to cope with this problem, thedescent portion 20 may be formed by the pressing of metal material. As aresult, the problem of machining expense of the descent portion 20 intime can be relieved.

There may be a problem that the machining of the descent portion 20requires much expense in time. In order to cope with this problem, thedescent portion 20 may be formed by pressing of metal material. As aresult, the problem of machining expense of the descent portion 20 intime can be relieved.

Further, the thrust dynamic pressure groove 23 may be formed at least atany surface of the disk portion 20A of the descent portion 20.Specifically, the thrust dynamic pressure groove 23 is formed at leasteither at the surface of the disk portion 20A opposed to the openingupper end surface of the housing 13 or the surface of the disk portion20A opposed to the overhanging member 19. As a result, machining of thethrust dynamic pressure groove 23 becomes easy.

Here, in accordance with thinning of the disk drive device 100, thestator core 11 is configured to be thin. When the stator core 11 becomesthin, there is a possibility that the stator core 11 is attached to beinclined when the circular portion thereof is fitted to the base member3. In order to cope with this problem, a stator core supporting member32 is disposed between the salient pole of the stator core 11 and thebase member 3. The stator core supporting member 32 is arranged tocircularly project from the base member 3 toward the salient pole of thestator core 11 at which the coil 12 is not arranged. As a result, thestator core 11 is supported at the inner circumference and the outercircumference. Accordingly, the problem of the stator core 11 incliningby the thinning is relieved.

A part of the hub 4 covering the outer circumference of the magnet 21performs a function of so-called back yoke. When the back yoke becomesthin, the magnetic resistance is increased. When the magnetic resistanceis increased, the magnetic flux which is generated by the magnet 21 isdecreased. When the magnetic flux is decreased, the torque is decreased.Accordingly, there may be a problem that a malfunction such as unstablerotation occurs. In order to cope with this problem, the hub 4 has theannular extension portion 4C, which extends outward, and the diameter106 of the outer circumference end of the annular extension portion 4Cis set to be larger than the diameter 90 of the interior cylinderportion 4D of the hub 4 by 4 mm or more. As a result, the thickness ofthe back yoke is sufficiently ensured and the problem caused by thetorque decrease is relieved.

Here, when strong magnetic material is used for increasing the torque,there is a case that leaked magnetic flux is increased due to magneticsaturation in the back yoke. When the leaked magnetic flux is increased,a noise signal may be generated at a magnetic head for reading/writingdata. When the noise signal is large, there is a possibility that normaloperation of reading/writing of magnetic data is impaired. In order tocope with this problem, the saturation magnetic flux density of theannular extension portion 4C, which functions as the back yoke, is setto be 1 T (tesla) or more. With this configuration, the saturationmagnetic flux density can be sufficiently ensured at the back yoke andthe problem of increasing of the leaked magnetic flux is relieved. Here,when the saturation magnetic flux density of the hub 4 is set to be 1.2T or more, stronger magnetic material can be used.

Here, there may be a demand to increase the torque so as to stabilizethe rotation. In order to cope with this demand, the opposing clearancebetween the distal end 11A of the salient pole and the magnet 21 is setto be 0.4 mm or less. Namely, a gap where the distal end 11A of thesalient pole and the magnet 21 face each other is set to be 0.4 mm orless. As a result, an air gap of the magnetic circuit becomes small andthe magnetic flux amount of the magnet 21 is increased so that thetorque is increased. The opposing clearance between the salient pole andthe magnet 21 is preferable to be 0.4 mm or less in view of ensuringeffect to increase the torque and to be 0.2 mm or more in view ofpreventing contact between the salient pole and the magnet 21.

Further, the maximum energy product of the magnet 21 according to thepresent embodiment may be set to be 10 megagauss-oersted (MGOe) or more.Accordingly, the magnetic flux amount of the magnet 21 is increased sothat the torque is increased. The maximum energy product of the magnet21 is preferably to be 10 MGOe or more in view of ensuring the torqueincreasing effect and to be 16 MGOe or less in view of easiness ofmagnetizing. Here, by combining the magnet 21 of the abovementionedmaximum energy product with the back yoke of which saturation magneticdensity is 1 T or more, the leaking of the magnetic flux from the backyoke can be suppressed even in the thinned disk drive device 100.

There is a demand of further thinning and lightening for the disk drivedevice 100 which is mounted on a portable apparatus. In order to copewith this demand, the inner diameter of the recording disk 1 is set tobe 20 mm and the thickness of the disk drive device in the axialdirection is set to be 7.5 mm or less. As a result, the portableapparatus can be configured to be thin and light. Further, it alsocontributes to resources saving.

As described above, the disk drive device 100 according to the presentembodiment can stabilize the rotation of the recording disk 1 whileachieving further thinning so as to be a preferable shape for a portableapparatus and the like.

Not limited to the abovementioned embodiments, the present invention ispossible to be modified by various design changes based on knowledge ofskilled persons. The configuration illustrated in each of the drawingsis simply for describing an example and can be appropriately modified sothat the similar effects are obtained as long as the similar functionscan be achieved.

1. A disk drive device comprising: a base member; a hub; a bearing unitwhich is arranged on the base member and which rotatably supports thehub; and a spindle drive unit which drives the hub to rotate, whereinthe spindle drive unit includes a stator core having a salient pole, acoil which is wound around the salient pole, and a magnet which isopposed to the salient pole; the hub formed of magnetic materialincludes an outer cylinder portion which is engaged with an innercircumference of a recording disk, and an inner cylinder portion towhich an outer circumference of the magnet is fixed; and the diameter ofthe inner cylinder portion is larger than the diameter of the outercylinder portion.
 2. The disk drive device according to claim 1, whereinthe diameter of a circle connecting salient ends of the stator core is80% or more of the diameter of the outer cylinder portion of the hub. 3.The disk drive device according to claim 1, wherein the base memberincludes a wire hole through which a wire for forming the coil ispassing; and the wire is guided via the wire hole to the back of thebase member surface on which the stator core is arranged, and isconnected to a wiring member at a position outside the outer diameter ofthe magnet in the radial direction.
 4. The disk drive device accordingto claim 1, wherein a channel portion which guides the wire via the wirehole for connecting to the wiring member at the back of the base membersurface on which the stator core is arranged; and the channel portion isinsulation treated.
 5. The disk drive device according to claim 1,wherein a surface of the coil opposed to the hub and a surface of thecoil opposed to the base member are leveled.
 6. The disk drive deviceaccording to claim 5, wherein the flattening ratio of the wire whichforms the leveled coil is 90% or less.
 7. The disk drive deviceaccording to claim 1, wherein a surface of the hub opposed to the coilis insulation treated.
 8. The disk drive device according to claim 1,wherein a surface of the base member opposed to the coil is insulationtreated.
 9. The disk drive device according to claim 1, wherein width inthe axial direction of the hub opposed to the coil is larger than widthin the axial direction of the base member opposed to the coil.
 10. Thedisk drive device according to claim 1, wherein the hub includes arecess portion on a surface of the side to which the recording disk ismounted and a threaded hole which is formed at the recess portion. 11.The disk drive device according to claim 10, wherein the threadedportion is formed to penetrate in the axial direction; and a covermember is disposed at a surface of the hub to which the threaded portionis formed and which is opposed to the coil.
 12. The disk drive deviceaccording to claim 1, wherein the bearing unit includes a shaft, asleeve into which the shaft is inserted and a housing into which thesleeve is inserted; and the housing is in the form of a cup with abottom such that a cylinder portion and a bottom portion are integrallyformed.
 13. The disk drive device according to claim 1, wherein thebearing unit further includes a descent portion which is rotatedintegrally with the hub and a overhanging member which is arranged so asto be nonrotatable at a position opposed to the descent portion in theaxial direction; the descent portion restricts movement of the hub inthe axial direction in cooperation with the overhanging member; andwidth in the axial direction of the descent portion opposed to theoverhanging member is 0.6 mm or less.
 14. The disk drive deviceaccording to claim 13, wherein the descent portion is formed byintegrating a disk portion which is opposed to the overhanging member inthe axial direction and a cylinder portion which is connected to theperiphery of the disk portion.
 15. The disk drive device according toclaim 14, wherein a thrust dynamic pressure groove is formed at least atany surface of the disk portion of the descent portion.
 16. The diskdrive device according to claim 1, wherein a stator core supportingmember is disposed between the salient pole of the stator core and thebase member.
 17. The disk drive device according to claim 1, wherein thehub includes a annular extension portion which extends outward; and thediameter of the annular extension portion is larger than the diameter ofthe inner cylinder portion by 4 mm or more.
 18. The disk drive deviceaccording to claim 1, wherein saturation magnetic flux density of thehub is set to be 1 T or more.
 19. The disk drive device according toclaim 1, wherein a gap where the salient pole and the magnet face eachother is set to be 0.4 mm or less.
 20. The disk drive device accordingto claim 1, wherein maximum energy product of the magnet is set to be 10MGOe or more.